The present disclosure relates generally to an engine control system and method, and particularly relates to a control system and method that controls engine air flow during a deceleration fuel cut.
It is known to cut fuel to an internal combustion engine during deceleration of the vehicle, e.g., sending a command signal to cease delivery of fuel to the combustion cylinders of the engine, where the command signal can be the vehicle's electronic control unit (ECU) directing one or more injector drivers to vary output voltage that drives one or more fuel injectors. In one conventional engine control system, the ECU controls intake air flow to the engine during such a fuel cut, such as by using drive-by-wire (DBW) throttle control. The purpose for controlling intake air flow during a deceleration fuel cut is to suppress blow-by gasses that would otherwise enter into the engine from the engine's crank case.
More particularly, with reference to FIG. 1, one cylinder 10 of a plurality of engine cylinders is schematically shown for internal combustion engine 12. During normal operation of the engine 12, the cylinder 10 receives combustion air through an intake port 14 from an upstream intake manifold 16. The combustion air delivered through the intake 14 combusts with fuel from fuel injector 17 in the cylinder 10 to move cylinder piston 18 in a known manner. Exhaust gases from the combustion process in the cylinder 10 are directed through an exhaust port 20 and ultimately through an exhaust manifold 22 operatively connected to the engine 12.
When fuel is cut during engine deceleration, no combustion occurs in the cylinder 10. In this state, the engine 12 acts solely as a pump. If left unchecked, a negative pressure situation can occur in the cylinder 10 leading to blow-by gases 24 entering the cylinder 10 from the crank case 26. This can be remedied by controlling intake air flow 28 into the engine 12 by controlling throttle 30. In particular, throttle valve 32 of the throttle 30 is controlled by a throttle controller 34 which receives command signals from ECU 36. Specifically, the amount of air flow let into the engine 12 by the throttle 30 is used to control the vacuum in the intake system, particularly in the cylinders of the engine 12, such as cylinder 10. That is, the throttle valve 32 is opened to create a positive pressure situation within the cylinder 10 to limit blow-by gases from venturing into the engine 12 from the crank case 26.
The amount of air flow 28 let into the engine 12 by the throttle valve 32 has a direct relationship to the amount of blow-by oil 24 that escapes from the crank case 26 and enters into the combustion chamber of the cylinder 10. Prior art engine control systems use a pre-calibrated table to look up how much air flow to allow into the engine 12 by the throttle 30 based on engine speed. For monitoring engine speed, an engine speed sensor 38 is typically provided on the engine's output shaft 40. Thus, the ECU 36 looks up the desired air flow to be delivered into the engine 12, and to the cylinders of the engine 12 (e.g., cylinder 10), to find the desired amount of air flow necessary to sufficiently limit blow-by gases from entering into the engine 12 based on a particular engine speed. The ECU 36 converts the looked-up desired air flow amount to a throttle angle for the throttle 30 and outputs a command signal to the throttle controller 34, which in turn adjusts the position of the throttle valve 32 accordingly.